(1) Field of the Invention
The present invention relates generally to a system and method for controlling engine revolutions for vehicular engines which carry out both the control of idling engine revolutions and boost pressure.
(2) Description of the Bakground Art
An engine revolution controlling system is previously proposed. in detail, an idling control valve which is driven by means of a control circuit is intervened in an auxiliary air passage bypassing a throttle valve of an engine.
An opening angle of the idling control valve controls an idling engine revolution to reach a target engine revolution. During engine deceleration, the idling control valve is opened such that an increase in an intake negative pressure (boost pressure) along with an abrupt close of the throttle valve results in an oil drop (leakage) from an intake and/or exhaust valve) can be prevented.
In addition, in such a previously proposed engine revolution controlling system as described above, an air regulator of a wax type is intervened in the auxiliary air passage whose opening angle is varied according to a temperature, in place of an idling control valve. Since the intake air quantity is increased according to a cooled state of the air regulator, an improvement in engine cranking and warmed up characteristics of the engine can be carried out.
The engine revolution controlling system as described above is exemplified by Japanese Patent Application Second Publication Showa, 61-15260 Published on Apr. 23, 1986, and the second Showa Japanese Patent Application Publication No. 62-50651, Published on Oct. 26, 1987.
In such a previously proposed engine revolution controlling system, when the engine deceleration condition is detected from the engine revolution speed and/or opening angle of the throttle valve, the idling control valve is widely opened such that an increase in the boost pressure can be prevented. In this case, to carry out the boost pressure control easily and with a good response characteristic, the idling control valve may previously be opened through a boost control opening angle which is determined according to the engine revolution speed.
However, although the prevention of an increase in the boost pressure can be achieved during the engine deceleration without sequential detection of the deceleration state, the engine revolution becomes increased more than necessary depending on a state of the air regulator.
That is to say, since the air regulator is opened during the cooling condition and the idling controlling valve is widely opened in such a state, the intake air quantity becomes too large. Therefore, in spite of the deceleration when driving, the engine revolution is not so reduced. In addition, even when the engine revolution is increased to some degree during the engine warm up, the idling control valve is accordingly opened. Thus, the idling revolution becomes considerably increased.